1. Field of the Invention
This invention relates generally to the field of automobile repair devices, and more particularly to a portable apparatus suitable for straightening or realigning the metal frame of a motor vehicle that has been involved in an accident.
2. Related Technology
The frame of an automobile that has been involved in a collision often undergoes plastic deformations. The vehicle cannot be operated safely unless these plastic deformations are removed and the vehicle frame returned to its original configuration. The realignment of the vehicle frame must be performed with a high degree of accuracy.
The state of the art method of straightening a vehicle frame involves securely anchoring the damaged vehicle and pulling the frame in a direction such that the vehicle frame is returned to its original configuration. The amount of force required must exceed the yield strength of the frame material, which is typically composed of a steel alloy. The tensile force is usually applied by means of a chain which is ultimately connected to a hydraulic cylinder capable of supplying the required force.
The damage to a vehicle frame can occur in any of a wide variety of magnitudes and orientations, and does not follow any set pattern. In order to correct the irregular damage actually encountered, the vehicle frame must be repeatedly pulled with varying amounts of force following many different vector paths. These numerous pulling operations are performed sequentially, and require that either the vehicle or the actual pulling mechanism be repeatedly repositioned as the frame straightening process progresses.
The repositioning steps consume a large portion of the time required to complete the overall frame repair. The vehicle frame apparatus must be quite sturdy in order to securely anchor the vehicle during the repeated pulling events. The typical frame straightening device usually includes some type of tower or standard which supports one end of a chain at some distance above the vehicle. Since some pulling vectors have a substantial vertical component, the tower should support its end of the chain at an elevation that is as high as possible. The other end of the chain is attached to the vehicle frame, and a hydraulic cylinder pulls the chain towards the tower. Ideally, this entire structure should be as sturdy, and hence massive, as possible.
However, many facilities in which frame straightening is performed do not have a sufficient volume of vehicle frame straightening work to justify dedicating an exclusive workspace, such as a garage bay, to this task. Thus, the frame straightening device should also be as small and portable as possible to facilitate its frequent manipulation during the frame straightening process as well as its removal from the area after the process is completed.
Some frame straightening devices secure the vehicle by anchoring the vehicle to a concrete floor. The vehicle perimeter is surrounded by a large number of anchors which can also support the pulling tower. As different pulling vectors are required, the tower can be moved to the nearest anchor position that approximates the desired azimuthal position. Such a system requires drilling a large number of permanent anchor sites into the concrete floor. The specific floor area adjacent to the anchor sites must be cleared whenever the frame straightening operation is to be performed. Since the number of anchor sites is finite, the number of pulls required to straighten the frame is increased, because two or more pulls are required to achieve the intermediate angle actually needed.
Other frame straightening devices have pulling standards that are connected to a work rack upon which the vehicle is secured. The standards are movable around the periphery of the work rack to provide various pulling angles. This type of device is generally large and quite massive. These devices are difficult to move, and usually remain permanently stationed in a certain area of designated floorspace.
Another solution is to mount a pivoting work rack onto a base frame. The pulling tower is mounted onto the base frame, and the work rack is rotated so as to provide the appropriate vectorial relationship between the vehicle frame and the tower. An example of such a device is disclosed in U.S. Pat. No. 5,031,438. The anchoring mechanism disclosed is limited to four portable jacks, which rely largely on the weight of the vehicle and the turntable itself to secure the turntable in place. Unless the chain is acting exactly along a diameter of the turntable, the turntable will tend to rotate when the pulling force exceeds the frictional force provided by the four jacks. This rotation is resisted only by a single longitudinal member and pin, which in practice can deflect or even break under the substantial loads imposed during a typical pulling operation. In order to rotate the turntable to a new position, all four jacks will frequently need to be raised through the substantial distance needed to clear the base member.
Another similar device is disclosed in U.S. Pat. No. 4,158,303, which includes a rotatable framework upon which the vehicle is mounted. In this device, the pulling tower is permanently interconnected to the base upon which the turntable is mounted. In order to anchor the entire structure, massive steel beams rest upon, but are not otherwise anchored to, the floor. While this may achieve the necessary stability required during pulling operations, the large mass of the device destroys its portability. Additionally, the rigid and permanent interconnection of the pulling tower to the base structure limits the absolute size of the frame which may be mounted on the turntable while still preserving its ability to rotate through a complete three hundred sixty degree arc.
The rotatable vehicle supports just described, as well as others, have not found wide acceptance in the industry because they are either to lightweight, too small, not portable and simply not versatile enough to satisfy the various demands placed on them in the course of operating an actual vehicle frame straightening business.